U.S. patent number 3,986,026 [Application Number 05/632,030] was granted by the patent office on 1976-10-12 for apparatus for proton radiography.
This patent grant is currently assigned to The United States of America as represented by the United States Energy. Invention is credited to Ronald L. Martin.
United States Patent |
3,986,026 |
Martin |
October 12, 1976 |
Apparatus for proton radiography
Abstract
An apparatus for effecting diagnostic proton radiography of
patients in hospitals comprises a source of negative hydrogen ions,
a synchrotron for accelerating the negative hydrogen ions to a
predetermined energy, a plurality of stations for stripping
extraction of a radiography beam of protons, means for sweeping the
extracted beam to cover a target, and means for measuring the
residual range, residual energy, or percentage transmission of
protons that pass through the target. The combination of
information identifying the position of the beam with information
about particles traversing the subject and the back absorber is
performed with the aid of a computer to provide a proton radiograph
of the subject. In an alternate embodiment of the invention, a back
absorber comprises a plurality of scintillators which are coupled
to detectors.
Inventors: |
Martin; Ronald L. (La Grange,
IL) |
Assignee: |
The United States of America as
represented by the United States Energy (Washington,
DC)
|
Family
ID: |
24533780 |
Appl.
No.: |
05/632,030 |
Filed: |
November 14, 1975 |
Current U.S.
Class: |
250/306; 315/503;
315/507; 250/358.1 |
Current CPC
Class: |
A61B
6/4258 (20130101); A61B 6/4092 (20130101); A61B
6/00 (20130101); G01N 23/04 (20130101) |
Current International
Class: |
A61B
6/00 (20060101); G01N 23/02 (20060101); G01N
23/04 (20060101); G01N 023/02 () |
Field of
Search: |
;250/306,307,358R
;313/359,363 ;328/235 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
proton Radiography in Tumor Detection, by Steward et al., from
Science, vol. 179 (1973), pp. 913, 914..
|
Primary Examiner: Borchelt; Archie R.
Attorney, Agent or Firm: Carlson; Dean E. Churm; Arthur A.
Reynolds; Donald P.
Government Interests
CONTRACTUAL ORIGIN OF THE INVENTION
The invention described herein was made in the course of, or under,
a contract with the UNITED STATES ENERGY RESEARCH AND DEVELOPMENT
ADMINISTRATION.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. An apparatus for performing diagnostic proton radiography of a
human subject comprising:
a source of negative hydrogen ions;
a synchrotron connected to the source to receive the negative
hydrogen ions and accelerate them in an orbit to a precisely
controlled predetermined value of energy;
means connected to the synchrotron for stripping the accelerated
negative hydrogen ions to produce a beam of protons and extract the
beam from the synchrotron;
means for disposing the human subject in the beam of protons;
means for sweeping the beam of protons in a predetermined pattern
to traverse a portion of the human subject;
a proton detector disposed to receive the portion of the beam that
traverses the human subject and to detect a parameter of the
protons received thereat; and
display means connected to the sweeping means and the detecting
means to produce from information about beam position and beam
intensity a proton radiograph of the subject.
2. The apparatus of claim 1 wherein the means for stripping
comprise:
a bumping magnet coupled to the accelerated beam and responsive to
a current to change the orbit of the accelerated beam; and
a fixed foil stripper disposed at the edge of the accelerated beam
in a location such that a change in the orbit in response to a
current in the bumping magnet moves the beam into contact with the
fixed foil stripper to remove electrons from the negative hydrogen
ions and convert them to protons.
3. The apparatus of claim 1 wherein the proton detector
comprises:
a beam stop of organic material disposed in the beam that traverses
the human subject to absorb all protons below a predetermined value
of energy;
a scintillator disposed in the beam that has traversed the beam
stop to detect protons traversing the subject and the beam stop;
and
a photomultiplier coupled optically to the scintillator to generate
an electric signal in response to scintillations therein.
4. The apparatus of claim 1 wherein the proton detector
comprises:
a plurality of scintillators disposed sequentially in the beam that
has traversed the human subject, and a plurality of
photomultipliers each coupled optically to one of said
scintillators and generating an electric signal in response to
scintillations therein, which electric signal is a function of the
parameters of the beam of protons passing through said
scintillator.
5. The apparatus of claim 1 wherein the display means comprise:
a computer to store information about proton count as a function of
beam position and means for making a plot of proton count as a
function of beam position, which plot is a proton radiograph of the
human subject.
6. The apparatus of claim 1 wherein the means for disposing the
human subject comprises a fixed support.
7. The apparatus of claim 1 wherein the means for disposing the
human subject comprise a rotating support.
8. An apparatus for making proton radiographs of an object
comprising:
a source of negative hydrogen ions;
a synchrotron connected to the source to receive the negative
hydrogen ions and accelerate them in an orbit to a precisely
controlled predetermined value of energy of the order of 200
MeV;
means connected to the synchrotron for stripping the accelerated
negative hydrogen ions to produce a beam of protons and extract the
beam from the synchrotron;
means for disposing the object in the beam of protons;
means for sweeping the beam of protons in a predetermined pattern
to traverse a portion of the object;
means for detecting a parameter of the beam of protons that has
traversed the object;
means for generating a visual display of the parameter as a
function of the predetermined pattern, which visual display is a
proton radiograph of the object.
9. The apparatus of claim 8 wherein the means for stripping
comprise:
a bumping magnet coupled to the accelerated beam and responsive to
a current to change the orbit of the accelerated beam; and
a fixed foil stripper disposed at the edge of the accelerated beam
in a location such that a change in the orbit in response to a
current in the bumping magnet moves the beam into contact with the
fixed foil stripper to remove electrons from the negative hydrogen
ions and convert them to protons.
10. The apparatus of claim 1 wherein the proton detector
comprises:
a plurality of scintillators disposed sequentially in the beam that
has traversed the object, and a plurality of photomultipliers each
coupled optically to one of said scintillators and generating an
electric signal in response to scintillations therein, which
electric signal is a function of the parameters of the beam of
protons passing through said scintillator.
Description
BACKGROUND OF THE INVENTION
This invention relates to proton radiography of human subjects.
Diagnostic radiologists are constantly seeking more useful
radiographs and other means for internal visualization that
minimize the risk of harm to patients. The detection by X-rays of
anomalies such as cancers and other tumors is rendered more
difficult by the fact that X-rays produce an image by absorption in
material through which they pass. This absorption is proportional
to the square of the atomic number of the material in the path of
the X-rays. Thus, bones, largely calcium, are easy to distinguish
and soft tissue, mostly carbon, hydrogen, and oxygen, is not. In
particular, cancerous lesions have very nearly the same atomic
composition as normal cells. Visualization of such lesions has
therefore been accomplished by injection or ingestion of a material
of high atomic number which will concentrate in the lesion to
increase its opacity to X-rays. A similar means of visualizing
lesions in certain parts of the human body involves the
administration of compounds containing radioisotopes that are taken
up preferentially by the lesions. Each of these means,
administration of dense compounds and administration of radioactive
compounds, presents a potential threat to the well-being of the
patient that would be better avoided if possible.
It is known that one way to avoid the threats outlined above is to
expose the suspected lesion to a flux of ions. It is possible to
detect differences in the energy loss in a beam of ions when the
beam is passed through a substance. This energy loss is
proportional to density, and in particular electron density. If a
lesions exhibits a difference in density from the surrounding
material, this density difference may be detected to provide a
picture of the lesion which would be difficult or impossible to
attain using X-rays. Other advantages exist from the use of ion
beams, particularly beams of protons. Since no tracer or radiopaque
material need be administered, there is no problem of delay in
obtaining pictures resulting from the time necessary to ingest and
distribute such tracer or radiopaque material. In addition, it has
proved possible to obtain proton radiographs using extremely low
levels of radiation.
The conclusions stated above have resulted from investigative work
that has been carried out at various Accelerator Laboratories. Each
such study has involved using an accelerator designed for research
in high-energy physics in a manner for which the accelerator is
marginally adapted. Relative to the needs of diagnostic proton
radiography, the particle-research accelerators are expensive to
build and complicated and expensive to operate. They produce too
many protons in a beam whose particle density across a cross
section is too high. The beam they produce is not designed either
to be swept or to be defocused into a uniformly diffuse beam.
Finally, and this is a serious disadvantage, they are not located
in or conveniently near hospitals. The combination of factors
outlined above suggests a need for a proton diagnostic accelerator
that is sufficiently inexpensive to build and simple to operate and
that is sufficiently safe that it can be located and routinely
operated in a hospital.
It is an object of the present invention to provide facilities for
proton radiography for location in a hospital.
It is a further object of the present invention to provide means
located in a hospital for obtaining diagnostic proton
radiographs.
Other objects will become apparent in the course of a detailed
description of the invention.
SUMMARY OF THE INVENTION
An apparatus for obtaining diagnostic proton radiographs of human
patients in a hospital comprises a source of negative hydrogen
ions, a synchrotron accelerator for accelerating the negative
hydrogen ions to an energy of the order of 200 MeV with a small
energy spread, a plurality of stripping stations for converting the
negative hydrogen ions to positive hydrogen ions in beams of
extremely high quality, means for sweeping each of the beams in a
raster covering a desired area, means for detecting energy changes
in the beam associated with soft tissue, and means for displaying
these changes as a function of position to produce a proton
radiograph of the soft tissue.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an overall schematic diagram of an apparatus for the
practice of the present invention.
FIG. 2 is an expanded view of the source and synchrotron of FIG.
1.
FIG. 3 is a schematic view showing the subject and the sweeping and
detection means of FIG. 1.
FIG. 3a is an alternate embodiment of the back absorber of FIG.
3.
FIG. 4 is an expanded view of the source of negative hydrogen ions
of FIG. 1.
FIG. 5 is a matrix of transmission percentages comprising a
radiograph of a sample of human tissue.
FIG. 6 is a radiograph constructed from the matrix of FIG. 5.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an overall sketch of an apparatus for the practice of the
present invention. In FIG. 1 source 10 is a generator of negative
hydrogen ions which are inserted into synchrotron 12 for
acceleration to a desired controlled energy. Strippers 14 convert
accelerated negative hydrogen ions to protons by removing the
electrons therefrom. The proton beam 16 that results from stripping
is caused by sweeping means 18 to execute a sweeping pattern or
raster on subject 20. Detection and display means 22 respond to the
protons that traverse subject 20 to produce therefrom a proton
radiograph of subject 20. A plurality of strippers 14, sweeping
means 18, and detection and display means 22 is shown in FIG. 1. In
one application of the present invention a proton radiograph will
be made of a subject by using one accelerated bunch of negative
hydrogen ions that is extracted as protons and is swept over an
interval of the order of one second. The plurality of strippers 14,
sweeping means 18 and detection and display means 22 facilitates
the placing and preparation of one or more patients while a
radiogram is being obtained of a subject patient.
FIG. 2 is an expanded view of the synchrotron 12 of FIG. 1. In FIG.
2 source 10 generates negative hydrogen ions which are deflected
for injection into synchrotron 12 by kicker magnet 30. Bending
magnet 32 and focusing quadrupole magnet 33 combine to bend and
focus the beam of negative hydrogen ions and are caused to receive
appropriately changing magnetic fields so that as the beam
undergoes acceleration from beam accelerator 34 the equilibrium
radius of the beam remains substantially the same at about 12 or 13
feet. Thus, after a number of passages through beam accelerator 34,
the magnetic field of bending magnet 32 will have been caused to
rise to a magnetic field of the order of 6 to 8 kiloGauss (0.6-0.8
Tesla). At this point bumping magnet 35 is energized at a desired
time to cause enough of a shift in the path of accelerated
particles to place some of the particles in contact with stripper
36, a fixed foil stripper. This strips electrons to convert the
negative hydrogen ions to protons which are then bent in the
opposite direction by the next following bending magnet 32. Before
the application of a bumping current to bumping magnet 35, the path
of the accelerating and accelerated beams is alternately in vacuum
straight sections 38 and vacuum curved sections 40. Vacuum straight
sections 38 carry the beam in a straight path when it is not
subject to the influence of a bending magnetic field. Vacuum curved
sections 40 carry the beam in a path that is an arc of a circle
when the path is subject to the centripetal acceleration associated
with the velocity of a charged particle in a uniform magnetic
field. Vacuum pumps 42 are connected to various vacuum straight
sections 38 to maintain the extremely high vacuum that is needed
for successful operation of such a synchrotron. This vacuum is of
the order of 10.sup..sup.-10 picoPascals or hundreds of picoTorrs
to minimize scattering and unwanted stripping of the negative
hydrogen ions during acceleration. The proton extraction is a part
of the same vacuum system and comprises a section 44 that is curved
in the opposite direction from vacuum curved section 40. This
results from the fact that protons are charged oppositely from
negative hydrogen ions and is the basis of the stripping extraction
which is an essential feature of the present invention.
Beam accelerator 34 comprises an r-f accelerating gap having a peak
voltage of the order of 100 volts at frequencies ranging from
approximately 500 kHz to approximately 10 MHz. The frequency of the
r-f excitation applied to beam accelerator 34 and the value of the
magnetic field of bending magnet 32 are controlled together by
controller 46 which maintains the radius of the accelerating and
accelerated beam at a position which keeps it within the vacuum
system. In maintaining this control of the position of the beam so
that the beam remains within the vacuum straight sections 38 and
the vacuum curved sections 40 bending magnets 32 may be constructed
as conventional magnets for alternating-gradient synchrotrons, with
gaps on adjacent magnet sections being beveled to place the
gradient of the magnetic field alternately inward and outward and
thus accomplish focusing together with bending. In the alternative,
bending magnets 32 may be constructed to produce a zero gradient of
the magnetic field with focusing supplied by a focusing quadrupole
magnet 33 of which there may be several in different locations.
These are alternatives for choice by the accelerator designer. The
least expensive design is expected to result from using the
conventional bevel to create nonuniform gaps in bending magnets 32
and hence to construct a combined-function alternating-gradient
synchrotron. This is in contrast to the separated-function
alternating-gradient synchrotron that uses focusing
quadrupoles.
FIG. 3 is a schematic view of a scanning station. In FIG. 3
sweeping means 18 is disposed near subject 20 to generate a swept
beam that will scan the desired portion of subject 20 with a total
of the order of 10.sup.8 protons. Sweeping means 18 includes
sweeping coil 50 which is a magnetic coil that operates in a
fashion similar to the magnetic sweeping coils of conventional
television sets. Sweeping means 18 also includes sweep current
supply 52 which applies a predetermined value of current to
sweeping coil 50 to generate a sweeping raster. The deflected beam
passes through vacuum window 54 and through subject 20 before
passing through back absorber 56 to strike back scintillator 58.
Back absorber 56 is selected of a material and of a thickness to
absorb those protons with energies below a threshold value of
energy that is close to the range of selective absorption of the
anomaly that is being viewed. Those protons that pass through the
subject and through back absorber 56 strike back scintillator 58
and are detected there by photomultiplier 59. Top scintillator 60
and side scintillator 62 are located to provide signals identifying
the position of the beam that passes through subject 20. In
general, it is not necessary to associate position with the signal
from back scintillator 58 and photomultiplier 59 since that
position will be known as a function of time from the knowledge of
the wave form of sweep current supply 52. Subject 20 may either be
fixed in place for the typical exposure which is expected to be of
the order of one second or he may be scanned in three dimensions by
causing a plurality of beams to traverse the area under
investigation while the subject is caused to rotate in those beams.
Rotation will be accomplished by affixing the subject to rotating
support 64 which is connected by shaft 66 to rotating drive 68.
Signals representing appropriate information are coupled from sweep
current supply 52, and rotating drive 68 to computer 70 which
processes information about beam location, proton count, and
subject position to provide a proton radiograph of the subject 20.
Information for the three-dimensional radiograph is expected to
take approximately 10 proton pulses, each containing about 10.sup.7
protons, over a time period of the order of 30 seconds.
Back absorber 56 of FIG. 3 has as one function the absorption of
protons to remove them from the beam that strikes back scintillator
58 for detection. Thus, the beam that scans subject 20 can be given
enough energy to assure that very few protons are absorbed in
subject 20, with the attendant increased risk of radiation injury
to subject 20. In its simplest form, back absorber 56 is a block of
a material that is uniform in thickness. An alternate embodiment of
back absorber 56 is shown in FIG. 3a, in which back absorber 56
includes the function of proton detection. In FIG. 3a, back
absorber 56 comprises a plurality of scintillators 71 disposed in
beam path 72. Each scintillator 71 is coupled optically to a
photo-multiplier 73 that generates an electrical signal in response
to scintillations in the associated scintillator. Each
photomultiplier is connected electrically by a cable 74 to computer
70 for processing of the electrical signals. The embodiment of FIG.
3a allows the scintillator 71 that provides the best image to serve
as the primary detector of transmitted protons and extends the
range of density variations that can be measured.
FIG. 4 is a schematic diagram and sketch of a generator of negative
hydrogen ions for supply and injection into the synchrotron of the
present invention. In FIG. 4 discharge voltage source 76 generates
an electrical voltage between electrodes 78. Hydrogen from gas
source 80 is admitted between electrodes 78 and the gas discharge
through the hydrogen generates protons, electrons, and negative
hydrogen ions. A negative accelerating electrode 82 attracts the
protons and the negative hydrogen ions and electrons are
accelerated by the positive accelerating electrode 84 under the
influence of the electric field between electrodes 82 and 84
generated by a negative voltage from accelerating voltage source
86. Electrons and negative hydrogen ions pass through aperture 89
into vacuum environment 90 which is the vacuum environment of the
accelerator. Many other configurations of generators of negative
hydrogen ions are known to exist. Injection bending magnet 92 then
directs a magnetic field having components perpendicular to the
paths of the negative hydrogen ions and the electrons. The
electrons, being lighter, are deflected more than the negative
hydrogen ions and are caused to curve into electron absorber 94.
The negative hydrogen ions follow beam path 96 for injection into
the accelerator. Electron absorber 94 must be designed to prevent
the passage of the X-rays that will be generated by impact of
electrons in the expected velocity range.
FIGS. 5 and 6 are two presentations of data obtained through the
use of a secondary proton beam of the Zero-Gradient Synchrotron at
Argonne National Laboratory. FIG. 5 is a matrix of the percent
transmission of a 1/4-inch proton beam through a specimen of
removed human tissue, and FIG. 6 is a radiograph of the proton
densities obtained by applying standard relaxation techniques to
the percentage figures of FIG. 5. The array of numbers of FIG. 5
was obtained using a single proton detector. The test specimen, a
removed human breast containing a tumor, was placed in a water box
having parallel sides that were disposed perpendicular to the beam.
The purpose of the water box was to assure a substantially constant
total thickness of material to be traversed by the proton beam.
This demonstrates the sensitivity obtainable by the use of the
proton and prevents variations in thickness from distorting the
data obtained. The water box described above was indexed a total of
22 steps horizontally and 19 vertically. At each of the positions
the specimen was stopped and irradiated with a proton beam, and the
percent transmission of protons was determined at that location.
The numbers in the array of FIG. 5 are appropriate for entry into
and storage in a computer for later reconstruction inao a
radiograph such as FIG. 6 for a graphic display of the data
determined. In FIG. 6, selected contours from the proton
transmission percentages of FIg. 5 are plotted to show the features
made apparent in the transmission data. In FIG. 6, region 102 is
that part of the water box that contains no part of the specimen.
Thus, a region with transmission percentages in the range of 16 to
20 exhibits the same proton transmission as water. Line 104 defines
the edge of the specimen which was a removed human female breast
containing a tumor. The tumor is distinctly visible in region 106
in which proton transmission percentages are in the range of 8 to
10. The tumor can be located in this one-dimensional proton
radiograph by relating it to the location of the mammary duct
outlined in region 108.
The proton radiograph shown in FIGS. 5 and 6 epitomizes some of the
disadvantages that the present invention is designed to overcome.
First, the proton radiograph of FIGS. 5 and 6 was obtained on a
large research accelerator that was operated at an energy level and
a proton density level below its capacity. The beam used to produce
FIGS. 5 and 6 had a diameter of approximately 1/4 inch which is
much larger than is desirable for effective resolution. That beam
was not movable with the equipment at hand, so that it was
necessary to index the specimen in a fixed beam in order to obtain
the data for reconstruction into a radiograph. The specimen was
located in an area that is hazardous to personnel during operation
of the equipment because of the radiation levels normally present.
It would be impossible to make a proton radiograph of a living
human subject on the accelerators at the Zero Gradient Synchrotron
without substantial modification of the equipment and serious
disruption of normal operation of the accelerator. Radiographs on
living human subjects (breast radiographs) have been taken with
protons at Harvard using a 160 Mev cyclotron and image
intensifiers, and at Berkeley (head) with an 800-Mev alpha beam.
Neither accelerator is suitable for hospital use.
It took 3 hours to accumulate the data for the proton radiograph
shown in FIG. 6. Subsequent radiographs of removed tissue samples
taken at Argonne with 1 mm proton beams from the 200 Mev booster
synchrotron required 20 minutes. Neither of the proton beams at
Argonne, nor those of any existing proton synchrotron or cyclotron
has a beam quality (the product of beam size and divergence angle)
suitable for sweeping across a reasonable area of a subject in a
period of 1 second. The present invention overcomes this limitation
of existing accelerators by using single turn injection of negative
hydrogen ions, low beam intensity, and stripping extraction.
* * * * *